學習分享，研究分享

SELECT 指令搭配 sys.dm_db_index_physical_stats 這個動態管理函示(DMF, Dynamic Management Function) 可以查出資料庫中所有索引的碎裂狀態，如下 T-SQL 語法：

SELECT OBJECT_NAME(dt.object_id)      ,
       si.name                        ,
       dt.avg_fragmentation_in_percent,
       dt.avg_page_space_used_in_percent
FROM
       (SELECT object_id                   ,
               index_id                    ,
               avg_fragmentation_in_percent,
               avg_page_space_used_in_percent
       FROM    sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL, NULL, 'DETAILED')
       WHERE   index_id <> 0
       ) AS dt --does not return information about heaps
       INNER JOIN sys.indexes si
       ON     si.object_id = dt.object_id
          AND si.index_id  = dt.index_id

索引重建與索引重組的時機如下:

索引重組的時機

• 檢查 External fragmentation 部分
  • 當 avg_fragmentation_in_percent 的值介於 10 到 15 之間
• 檢查 Internal fragmentation 部分
  • 當 avg_page_space_used_in_percent 的值介於 60 到 75 之間

索引重建的時機

• 檢查 External fragmentation 部分
  • 當 avg_fragmentation_in_percent 的值大於 15
• 檢查 Internal fragmentation 部分
  • 當 avg_page_space_used_in_percent 的值小於 60

 自動幫你算出哪些索引需要被重建或重組，而且直接幫你把 ALTER INDEX 的 T-SQL 都寫好，程式碼如下：

SELECT 'ALTER INDEX [' + ix.name + '] ON [' + s.name + '].[' + t.name + '] ' +
       CASE
              WHEN ps.avg_fragmentation_in_percent > 15
              THEN 'REBUILD'
              ELSE 'REORGANIZE'
       END +
       CASE
              WHEN pc.partition_count > 1
              THEN ' PARTITION = ' + CAST(ps.partition_number AS nvarchar(MAX))
              ELSE ''
       END,
       avg_fragmentation_in_percent
FROM   sys.indexes AS ix
       INNER JOIN sys.tables t
       ON     t.object_id = ix.object_id
       INNER JOIN sys.schemas s
       ON     t.schema_id = s.schema_id
       INNER JOIN
              (SELECT object_id                   ,
                      index_id                    ,
                      avg_fragmentation_in_percent,
                      partition_number
              FROM    sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL, NULL, NULL)
              ) ps
       ON     t.object_id = ps.object_id
          AND ix.index_id = ps.index_id
       INNER JOIN
              (SELECT  object_id,
                       index_id ,
                       COUNT(DISTINCT partition_number) AS partition_count
              FROM     sys.partitions
              GROUP BY object_id,
                       index_id
              ) pc
       ON     t.object_id              = pc.object_id
          AND ix.index_id              = pc.index_id
WHERE  ps.avg_fragmentation_in_percent > 10
   AND ix.name IS NOT NULL